Disk drives are widely used in computers and data processing systems for storing information in digital form. These disk drives commonly use one or more rotating storage disks to store data in digital form. Each storage disk typically includes a data storage surface on each side of the storage disk. These storage surfaces are divided into a plurality of narrow, annular regions of different radii, commonly referred to as “tracks”. The disk drive includes a head stack assembly having a positioner, an actuator assembly and one or more transducer assemblies. The actuator assembly includes an actuator hub, an actuator pivot center, and one or more actuator arms. Each transducer assembly includes one or more data transducers. The positioner is used to precisely rotate the actuator assembly to position the data transducers relative to one or more storage disks. The data transducer transfers information to and from the storage disk when precisely positioned over an appropriate data track (also referred to herein as a “target track”) of the storage surface.
The need for increased storage capacity and compact construction of the disk drive has led to the use of disks having increased track density, i.e. more tracks per inch. As the track density increases, the ability to maintain the data transducer over the target track becomes more difficult. More specifically, as track density increases, it is necessary to reduce positioning error of the data transducer proportionally. With these systems, the accurate and stable positioning of the data transducer proximate the appropriate track is critical to the accurate transfer and/or retrieval of information from the rotating storage disks.
Conventional positioners which include the use of a voice coil motor are well known. The voice coil motor works by directing electrical current through a wound wire coil located in a magnetic field. Besides causing the actuator arms and transducer assemblies to move in a desired direction, the same coil forces excite one or more undesirable vibration modes, including for example, a “first vibration mode” and a “second vibration mode”. In some drives, the first vibration mode can occur at a frequency of between approximately 5,000 and 7,500 cycles per second and the second vibration mode can occur at a frequency of between approximately 7,500 and 12,000 cycles per second, although these frequencies can vary depending upon the design of the disk drive. Either or both of these vibration modes can cause an undesirable resultant force (hereinafter “FR”) at the actuator hub, which when unaccounted for, can result in a vibration displacement of the data transducer. The vibration displacement of the data transducer can cause difficulty in accurately positioning and/or maintaining the positioning of the data transducer over the desired track of the storage disk. The first and/or second vibration modes are caused at least in part by the structural response of the actuator assembly to forces from the coil that are used to position the data transducers.
One attempt to increase the level of accuracy in positioning the actuator assembly and the transducer assembly relative to the storage disk includes using a so-called “pure torque” positioner, i.e. generating theoretical force vectors with one or more coils that are equal but directionally opposite relative to the actuator hub, so that the forces have a sum total of zero at the actuator hub. In theory, if the forces effectively offset each other, presumably no excitation of the first and second vibration modes at the actuator hub, and thus no resultant force FR at the actuator hub will occur. Importantly, however, this theory assumes that the positioner and the actuator assembly are a purely rigid, completely inflexible body, and the first and second vibration modes are rigid body translation motions. Unfortunately, because the positioner and the actuator assembly are not completely rigid, either or both of the first and/or second vibration modes are not satisfactorily inhibited and a resultant force FR on the actuator hub consequently remains.
In light of the above, the need exists to provide a high bandwidth positioner that accurately positions and/or maintains the position of one or more data transducer(s) relative to the target track. Another need exists to provide a positioner that inhibits excitation of the first and/or second vibration modes, and thus, the resultant force FR at the actuator hub. Still another need exists to reduce the cost of manufacturing a high performance, high-density disk drive.